The invention relates to a magnetic-tape apparatus having a tape-drive shaft which can be driven in a rotating fashion to drive a magnetic tape, and having a pressure-roller device, in the case of which a substantial feature is provided by virtue of the fact that the pressure roller is mounted with the aid of two bearing surfaces which are formed in each case by a toroidal surface and which give the pressure roller freedom of movement for matching the axial direction of the pressure roller to the axial direction of the tape-drive shaft.
The invention further relates to a pressure-roller unit, in which a substantial feature consists in that the pressure roller is mounted with the aid of two bearing surfaces each formed by a toroidal surface, which bearing surfaces of the pressure roller give freedom of movement for matching the axial direction of the pressure roller to a desired direction.
Reference may be made to patent document U.S. Pat. No. 5,452,833 A in the connection set forth above in the first paragraph and the second paragraph. This patent document discloses a magnetic-tape apparatus having a pressure-roller device and a pressure-roller unit, the pressure roller being mounted with the aid of two toroidal surfaces. In the design disclosed in patent document U.S. Pat. No. 5,452,833 A, a bearing part for rotatably bearing the bearing roller is rotatably held on a pressure-roller spindle, and the bearing part is thereby provided with an external toroidal surface which cooperates with an internal toroidal surface which is provided in a bearing sleeve located in the interior of the pressure roller. In this case, the design is made such that a sufficiently large play is provided between the two toroidal surfaces, that is to say between the external toroidal surface of the bearing part and the internal toroidal surface of the pressure roller, which must necessarily be the case with this solution, because without this play a matching movement, that is to say a wobbling movement of the pressure roller relative to the bearing part would not be possible at all. It may be expressly pointed out here that in the case where two toroidal surfaces provided as bearing surfaces are provided in virtually rigid bodies and thereby lie against one another virtually without play, no wobbling movements at all are possible, but only a pure rotational movement. The reason for this lies in the geometry of toroidal surfaces. In the known design, sufficiently large play is thereby deliberately provided between the two toroidal surfaces provided as bearing surfaces, in order to permit a wobbling movement of the pressure roller.
The design described in patent document U.S. Pat. No. 5,452,833 A has proved to be an acceptably functioning solution during the driving of a magnetic tape with the aid of the tape-drive shaft and the pressure roller. In the case of the known solution, however, it has emerged that at each instant at which the pressure roller is brought into operational connection with the tape-drive shaft the play present between the two toroidal surfaces and, to be precise in this case, the axial component of this play, constitute a problem, specifically because at the instant when the pressure roller presses against the tape-drive shaft an axial movement of the pressure roller comes about, admittedly only slight but occurring nevertheless, which axial movement has, or can have the consequence that the tape present between the pressure roller and the tape-drive shaft is also moved slightly in the axial direction of the tape-drive shaft, that is to say transverse to the tape longitudinal direction, and this has a disadvantageous effect on the scanning operation of the magnetic tape. This problem appears in a disturbing way in particular whenever the magnetic tape is driven in what is termed the start-stop mode, in which a continuously repeating alternation between pressure from the pressure roller against the tape drive roller and lifting of the pressure roller from the tape-drive shaft takes place in short time intervals.
The invention has set itself the object of removing the problems set forth above in a structurally simple way and with simple means, and of implementing an improved magnetic-tape apparatus and an improved pressure-roller unit.
In order to achieve the object set forth above, in the case of a magnetic-tape apparatus according to the invention features according to the invention are provided such that a magnetic-tape apparatus according to the invention can be defined in the following given way, specifically:
A magnetic-tape apparatus having a tape-drive shaft which can be driven in a rotating fashion to drive a magnetic tape, and having a pressure-roller device which has a pressure roller, that can be pressed against the tape-drive shaft, and an adjustable pressure-roller carrier, and a pressure-roller spindle borne by the pressure-roller carrier, and a bearing part, which surrounds the pressure-roller spindle and can be rotated relative to the pressure-roller spindle, for rotatably bearing the pressure roller, the bearing part having a first bearing surface which is formed by a toroidal surface, and in which the first bearing surface of the bearing part is operationally connected to a second bearing surface of a counterbearing which is likewise formed by a toroidal surface, and in which the two bearing surfaces, formed in each case by a toroidal surface, of the pressure roller give freedom of movement for matching the axial direction of the pressure roller to the axial direction of the tape-drive shaft, and in which the two bearing surfaces are held lying against one another without play, and in which of these two bearing surfaces at least one bearing surface is provided in a compliant fashion in radial directions relative to the other bearing surface.
In order to achieve the object set forth above, in the case of a pressure-roller unit in accordance with the invention features according to the invention are further provided such that a pressure-roller unit in accordance with the invention can be defined in the way specified below, specifically:
A pressure-roller unit for a magnetic-tape apparatus having a drive shaft which can be driven in a rotating fashion to drive a magnetic tape, which magnetic tape can be pressed against the tape-drive shaft with the aid of a pressure roller of the pressure-roller unit, which pressure-roller unit has a pressure roller and a pressure-roller spindle and a bearing part, which surrounds the pressure-roller spindle and can be rotated relative to the pressure-roller spindle, for rotatably bearing the pressure roller, in which the bearing part has a first bearing surface which is formed by a toroidal surface, and in which the first bearing surface of the bearing part is operationally connected to a second bearing surface of a counterbearing which is likewise formed by a toroidal surface, and in which the two bearing surfaces, formed in each case by a toroidal surface, of the pressure roller give freedom of movement for matching the axial direction of the pressure roller to a desired direction, and in which the two bearing surfaces are held lying against one another without play, and in which of these two bearing surfaces at least one bearing surface is provided in a compliant fashion in radial directions relative to the other bearing surface.
The result of the provision of the features in accordance with the invention is that in a structurally simple and space saving and cost effective way the pressure roller can be adapted both smoothly and quickly in terms of position to the alignment of the tape-drive shaft of a magnetic-tape apparatus according to the invention, and that it is also thereby ensured, however, that the pressure roller is held with the aid of the bearing surfaces formed by toroidal surfaces in an accurate and always reproducible starting position, it thereby being advantageously achieved that when the pressure roller is pressed against the tape-drive shaft the pressure roller cannot be adjusted axially relative to the tape-drive shaft, and therefore the undesired phenomena caused by such an axial readjustment are reliably avoided.
In the case of a magnetic-tape apparatus in accordance with the invention, it is possible to provide a design which corresponds to the design disclosed in patent document U.S. Pat. No. 5,452,833 A to the effect that a bearing part provided with an external toroidal surface and a bearing sleeve provided with an internal toroidal surface and located in the interior of the pressure roller are provided, although in accordance with the invention present here the two toroidal surfaces are held lying against one another without play and at least one of the two toroidal surfaces is provided in a compliant fashion in radial directions relative to the other of the two toroidal surfaces. It has proved particularly advantageous, however, when the design is as claimed in claim 2 or claim 12. This has proved to be particularly advantageous with regard to a design which is structurally very simple and satisfactory with a few components.
In an embodiment in accordance with the invention, it has proved, furthermore, to be particularly advantageous when the features as claimed in claim 3 or with claim 13 are additionally provided. Such a design offers the advantage that such a sleeve can be implemented as a plastic part in a simple way.
In an embodiment in accordance with the invention having a sleeve as described above, it has proved to be advantageous when the features as claimed in claim 4 or claim 14 are additionally provided. In this case, the compliance is implemented in the region of the counterbearing surface, specifically in a very simple way.
In an embodiment in accordance with the invention, it has proved to be particularly advantageous, however, when the features as claimed in claim 5 or claim 15 are additionally provided. Such a design is distinguished by a particular simplicity and, however, additionally also by a high stability and long lasting reliability.
There are various solutions for implementing a bearing surface which is provided on the bearing part and compliant in radial directions. However, it has proved to be particularly advantageous when a design having the features as claimed in claim 6 or claim 16 is implemented in this context. Such a design can be implemented in a structurally simple way, specifically in particular using plastic technology.
In an embodiment having at least two bearing part sectors, it has proved to be particularly advantageous when the features as claimed in claim 7 or in accordance with claim 17 are additionally provided. Such a design has proved to be particularly favorable in practice.
In an embodiment as mentioned above, it has proved to be particularly advantageous when the features as claimed in claim 8 or claim 18 are additionally provided and/or the features as claimed in claim 9 or claim 19. This is advantageous with regard to the stablest possible holding and bearing of the pressure roller.
In an embodiment having three holding part sectors, it has further proved to be very advantageous when the features as claimed in claim 10 or claim 20 are additionally provided. Such an embodiment offers the advantage of effectively sealing the bearing region having the toroidal surfaces off from the outer region of the pressure roller.
The aspects set forth above and further aspects of the invention proceed from the examples of embodiment described below and are explained with the aid of these exemplary embodiments.